Buyer guideDDA Range
Why DDA Handrails Are 42.4mm: Tube Diameter, Grip and Upright Spacing
The Building Regulations recommend a handrail diameter of 40mm to 45mm, and 42.4mm o/d (size 7) is the one stocked tube size inside that band. The rail is sized for the hand, the posts for the load, and upright spacing depends on the design load.
The Building Regulations recommend a handrail outside diameter of between 40mm and 45mm. Of the five tube sizes we stock, one sits inside that band: 42.4mm o/d, size 7 in trade sizing. That is the whole reason the DDA handrail range is built around it. For the full set of rules, see the requirements a DDA handrail has to meet.
The more useful questions are how the rail is carried and how far apart the posts go, because that is where most ordering mistakes happen.
The Five Stocked Sizes
We stock five sizes of key clamp fitting and galvanised steel tube, numbered 5 to 9, from 26.9mm to 60.3mm outside diameter.
| Size | Tube o/d | Nominal bore | Typical use |
|---|---|---|---|
| 5 | 26.9mm | 3/4″ | Light structures, infill |
| 6 | 33.7mm | 1″ | Shop-fit, garment rail, display, light barrier |
| 7 | 42.4mm | 1 1/4″ | DDA handrail, handrail and guardrail |
| 8 | 48.3mm | 1 1/2″ | Uprights, guardrail, main structure |
| 9 | 60.3mm | 2″ | Heavy structure, long spans |
Every fitting code ends in the size, so an A2-7 is an A2 short tee for size 7 (42.4mm) tube. Quote in sizes or millimetres and we will match it.
Why 42.4mm for the Rail
A handrail is not a structural member you happen to be able to touch. It is a thing people grip, and the grip is the specification.
At 42.4mm, a hand closes around the tube with the fingers meeting the thumb. That matters for a user with reduced grip strength, arthritis, or a hand that is taking real weight rather than steadying a stride. Move up to 48.3mm and the hand no longer closes; the rail becomes something to rest a palm on, which is a different and weaker action. Move down to 33.7mm and there isn’t enough section for a confident hold.
The 40mm to 45mm band in the Building Regulations reflects that narrow window. 42.4mm sits in the middle of it and is a standard stocked tube size, so no specially drawn section is needed.
How the Rail Is Carried
The rail is sized for the hand. The posts are sized for the load. Different job, and often a different tube.
In our DDA range the rail sits on handrail brackets, the DDA747 and DDA748, each used with an A6-7 elbow or an A2-7 short tee, so the hand runs along the rail without meeting a clamp. Along a wall, the DDA745 and DDA746 wall brackets do the same job. More on why that matters in continuous DDA handrails.
Where the rail also guards a drop, size the posts and their spacing for the design load, using the table below.
Wall Thickness for Internal Fittings
The DDA725 internal 90 degree elbow, the DDA09 internal variable elbow and the A9 internal connector all sit inside the tube, which is what keeps the grip surface smooth. They suit medium weight tube with a maximum wall thickness of 3.2mm.
Two rules apply to the A9 internal connector:
- Joints must be within 150mm of the nearest support
- Do not use it to join tubes under extreme loads or a direct tensile load
Upright Spacing and Design Load
This is the part that gets missed, and it is the part that matters structurally.
The load capacity of a handrail or guardrail is governed principally by the diameter, wall thickness and frequency of the uprights. Not by the rail. Wider post spacing means less capacity, on the same tube, at the same height.
Design loads are usually stated in the specification. Where they aren’t, BS 6180 and BS 6399 are the reference documents.
The maximum upright centres below are for a 1100mm high guardrail, in millimetres:
| Design load | 33.7 × 3.2 | 42.4 × 3.2 | 42.4 × 4.0 | 48.3 × 3.2 | 48.3 × 4.0 | 48.3 × 5.0 |
|---|---|---|---|---|---|---|
| 360 N/m | 666 | 1120 | 1305 | 1496 | 2114 | 2778 |
| 740 N/m | 324 | 545 | 635 | 728 | 1028 | 1824 |
| 1500 N/m | 160 | 269 | 313 | 359 | 507 | 900 |
Read across before you order. The difference between the 0.36 kN/m and 1.5 kN/m categories on 48.3 × 3.2mm tube is 1496mm of spacing against 359mm: more than four times as many posts for the same run. A handrail specified at one design load and built at the spacing for another looks identical on site and behaves entirely differently under load.
On standard guardrail, rails need only be 3.2mm wall. Where the assembly has to satisfy a higher category, the answer is usually thicker-walled uprights rather than closer posts, because posts are what you notice.
What the Fittings Themselves Will Take
Fisher Alvin key clamps are malleable iron castings manufactured in excess of BS 6681 (ISO 5922) and BS 2789 (ISO 1083), supplied with Dacromat coated, case hardened set screws. When tightened to 29 ft lb (4.1 kgm), a slip load of 900kg can be obtained on each screw.
Use a torque wrench rather than judging it by feel. A hexagon key gets the fitting on, but it won’t tell you when you’ve reached the right torque.
Ordering Without Getting It Wrong
Tube is cut to length in-house before despatch, free of charge. Send the cutting list with the order and it arrives ready to assemble, which removes the cutting and the waste from site.
One practical note on the castings: because these are galvanised castings, the published dimensions cannot be exact. Do not pre-drill bolt holes before the fittings are on site. Set the fitting, then mark and drill.
If you’re unsure which size does which job on your layout, send us the drawing or a sketch. We’ll come back with the fittings and cutting list. Request a quote and we reply within one hour in working hours, or call 01905 779944.
Handrail Tube Size FAQs
What Size Tube Is a DDA Handrail?
42.4mm outside diameter: size 7, 1 1/4″ nominal bore. The Building Regulations recommend an o/d of between 40mm and 45mm, and 42.4mm sits in the middle of that band.
How Is the Rail Fixed to the Posts?
With DDA747 or DDA748 handrail brackets, each used with an A6-7 elbow or A2-7 short tee, so the hand never meets a clamp. Along a wall, use DDA745 or DDA746 wall brackets.
What Tube Sizes Does Fisher Alvin Stock?
Five, numbered 5 to 9: 26.9mm, 33.7mm, 42.4mm, 48.3mm and 60.3mm outside diameter, with fittings to match each.
What Wall Thickness Do Internal Fittings Need?
The DDA725, DDA09 and A9 sit inside the tube and suit medium weight tube with a maximum wall thickness of 3.2mm.
How Far Apart Should Handrail Uprights Be?
It depends on the design load, the tube size and wall thickness, and the rail height. At 1100mm high on 48.3 × 3.2mm tube, maximum centres run from 1496mm at 360 N/m down to 359mm at 1500 N/m. Check the design load in your specification before setting out.
How Much Load Will a Key Clamp Fitting Take?
When tightened to 29 ft lb (4.1 kgm), a slip load of 900kg can be obtained on each screw.
Can I Pre-Drill the Baseplate Holes Before Delivery?
No. These are galvanised castings and the published dimensions cannot be precise, so pre-drilled holes rarely line up. Set the fitting in position, then mark and drill.
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